Fixed type constant velocity universal joint

ABSTRACT

A fixed type constant velocity universal joint has outer joint member track grooves each with a raceway center line that includes an arc-shaped portion having a curvature center that has no offset with respect to a joint center in an axial direction. The track grooves are formed such that adjacent track grooves are inclined in opposite directions. The joint also has inner joint member track grooves that are each formed to be mirror-symmetric with a corresponding one of the outer joint member track grooves with a plane including the joint center and being orthogonal to the axis of the joint at an operating angle of 0°. When at a large operating angle, an operating angle at which a torque transmission ball loses contact with the inner joint member track groove is larger than that at which the torque transmission ball loses contact with the outer joint member track groove.

TECHNICAL FIELD

The present invention relates to a fixed type constant velocityuniversal joint.

BACKGROUND ART

In a constant velocity universal joint, which is used to construct apower transmission system for automobiles and various industrialmachines, two shafts on a driving side and a driven side are coupled toeach other to allow torque transmission therebetween, and rotationaltorque can be transmitted at a constant velocity even when the twoshafts form an operating angle. The constant velocity universal joint isroughly classified into a fixed type constant velocity universal jointthat allows only angular displacement, and a plunging type constantvelocity universal joint that allows both the angular displacement andaxial displacement. In a drive shaft configured to transmit power froman engine of an automobile to a driving wheel, for example, the plungingtype constant velocity universal joint is used on a differential side(inboard side), and the fixed type constant velocity universal joint isused on a driving wheel side (outboard side).

As functions required for a fixed type constant velocity universal jointfor a drive shaft of an automobile, it is important to include a largeoperating angle, which conforms to the steering of wheels, and astrength suitable for the large operating angle. In the related art, ingeneral, a Rzeppa constant velocity universal joint (BJ type) has amaximum operating angle of 47°, and an undercut-free constant velocityuniversal joint (UJ type) has a maximum operating angle of 50°. From theviewpoint of improving the turning performance of an automobile andimproving ease of tight turns, there have been increasing demands for amaximum operating angle larger than 50°. In order to meet those demands,fixed type constant velocity universal joints of various structure havebeen proposed.

In Patent Document 1, it is described that, in a related-art fixed typeconstant velocity universal joint, at the time of the maximum operatingangle, regarding a torque transmission ball (hereinafter simply referredto as “ball”) located at a phase angle (phase angle)0° at which the ballmoves most toward an opening side of the outer joint member, a ratio ofan axis parallel distance between a center of the ball and a jointcenter to an axis parallel distance between the center of the ball andan opening conical surface of the outer joint member is set to be lessthan 2.9, thereby being capable of maintaining the function even at thetime of the maximum operating angle. Further, it is also described that,in a case in which the operating angle is taken so that the ballprojects to such an extent of losing a contact from the track groove ofthe outer joint member, the function can be maintained by setting theratio to be less than 2.2.

In Patent Document 2, as a countermeasure to be taken when a ball thathas lost a contact with a track groove returns to any one of the trackgroove of an outer joint member and the track groove of an inner jointmember, there is proposed a configuration in which an axial end portionof any one of the track groove of the outer joint member and the trackgroove of the inner joint member is formed into such a shape as toprevent the ball from transmitting torque. With this configuration,damage to an end portion of the outer joint member can be prevented.

In Patent Document 3, there is proposed not a fixed type constantvelocity universal joint having the maximum operating angle set to belarger than a hitherto-adopted operating angle (50°), but a fixed typeconstant velocity universal joint having high efficiency and having thestructure in which a raceway center line of each of track grooves of anouter joint member and a raceway center line of each of track grooves ofan inner joint member each include an arc-shaped portion having acurvature center that has no offset with respect to a joint center O inan axial direction, and in which the arc-shaped raceway center lines areinclined in opposite directions in a circumferential direction.

PRIOR ART DOCUMENTS Patent Documents

Patent Document 1: JP 4885236 B2

Patent Document 2: US 2009/0269129 A1

Patent Document 3: JP 2013-104432 A

SUMMARY OF THE INVENTION Problems to be Solved by the Invention

When a fixed type constant velocity universal joint having a maximumoperating angle larger than that of the hitherto-adopted operating angle(50°) is to be used, it is required that a length of the outer jointmember be set short so as to prevent interference between anintermediate shaft and the outer joint member. However, as a result,track grooves of the outer joint member become shorter, and a balllocated around the phase angle of 0° comes off the track groove andloses a contact.

In Patent Document 1, through setting of the ratio of the axial distancebetween the center of the ball and the joint center at a phase (phaseangle of0°) at which the ball projects most from an opening-side endportion of the outer joint member at the time of the maximum operatingangle, to the axial distance between the center of the ball and theopening conical surface of the outer joint member, the ball can beprevented from being dropped off from the cage and the outer jointmember. However, the track groove of the inner joint member remains onthe back side, and hence the ball moves along the track groove of theinner joint member toward a radially outer side of the cage. Thus, thereis a risk in that the ball loses a contact with the cage depending on ashape of the track groove such as an S shape or a linear shape.Accordingly, it has been found that retention of the ball is lost andnoise is generated.

In Patent Document 2, through adoption of the configuration in which thetrack groove is formed into such a shape as to prevent the ball fromtransmitting torque (or to bear no load) when the ball that has lost acontact with the track groove of the outer joint member returns to thetrack groove of the outer joint member again, damage to the opening-sideend portion of the outer joint member can be prevented. However, in acase in which the track groove is formed into such a shape as to bear noload of the ball when the ball returns to the track groove of the outerjoint member again, the balls located at other phases bear the load. Inparticular, the ball that has moved most toward the back side of theouter joint member, that is, the ball located at a phase angle of 180°bears most of this load. Accordingly, it has been found that the load tobe applied to the ball is increased, with the result that the outerjoint member and the inner joint member may be damaged early.

The fixed type constant velocity universal joint of Patent Document 3 isreduced in torque loss and generation of heat, and has high efficiency.However, there is an unknown problem when the fixed type constantvelocity universal joint is used at a large operating angle larger thanthe hitherto-adopted operating angle (50°). This problem is studied andinspected as described later.

In view of the problems described above, the present invention has anobject to provide a fixed type constant velocity universal joint, whichhas the maximum operating angle set to be larger than thehitherto-adopted operating angle (50°), has an operation mode in which,when a large operating angle is taken, a ball loses a contact in a rangeof a phase (phase angle of0°) at which the ball projects from an outerjoint member, and is capable of securing a constant velocitycharacteristic, transmission efficiency, and durability.

SOLUTIONS TO THE PROBLEMS

The inventors of the present invention have conducted extensive studiesand inspections for the problems described above, and obtained thefollowing knowledge and ideas, thereby achieving the present invention.

(1) Disturbance of a Balance of Forces in a Joint when a Ball Loses aContact

When the fixed type constant velocity universal joint is used at a largeoperating angle larger than the hitherto-adopted operating angle (50°),as described above, the track grooves of the outer joint member arereduced in length, and the ball located around the phase angle of 0°comes off the track groove and loses a contact. Further, in the phaserange in which the ball loses a contact with the track groove, a contactforce between the ball and the track groove of the outer joint member, acontact force between the ball and the track groove of the inner jointmember, and a force applied to the cage by the ball are lost, and theother balls bear the load, with the result that a balance of internalforces is disturbed. It has been found that, particularly in a type inwhich a curvature center of the track groove is offset in an axialdirection (hereinafter, also referred to as “axial track offset type”),such as a Rzeppa constant velocity universal joint (BJ type) or anundercut-free constant velocity universal joint (UJ type), a balance offorces in the constant velocity universal joint is significantlydisturbed.

(2) Consideration to Disturbance of the Balance of Forces in the Joint

In the fixed type constant velocity universal joint of the axial trackoffset type, the curvature center of the track groove of the outer jointmember is offset with respect to the joint center O toward the openingside of the outer joint member. Meanwhile, the curvature center of thetrack groove of the inner joint member is offset in a direction oppositeto that of the curvature center of the track groove of the outer jointmember. The ball is arranged in a wedge-shaped space opened toward theopening side and defined between the track groove of the outer jointmember and the track groove of the inner joint member, and is positionedby the cage.

Consideration is given as follows. When torque is applied at a smallangle about a normal operating angle, by component forces of the contactforces between the ball and the track groove of the outer joint memberand between the ball and the track groove of the inner joint member,each ball pushes the cage in the same direction. Thus, a spherical outerperipheral surface and a spherical inner peripheral surface of the cageare firmly brought into contact with a spherical inner peripheralsurface of the outer joint member and a spherical outer peripheralsurface of the inner joint member, respectively. When torque is appliedin a range of from a medium angle to a large angle, there are variationsin magnitude of the contact forces between each ball and the trackgroove of the outer joint member and between each ball and the trackgroove of the inner joint member, and there are also variations inmagnitude of the forces of pushing the cage by the balls. Thus, abalance of a moment applied to the cage is also slightly displaced froma bisecting plane. Moreover, at a large operating angle at which theball loses a contact with the track groove of the outer joint member,the number of the balls bearing the load is reduced. As a result, thebalance of the moment applied to the cage significantly changes so thatthe cage is significantly displaced from the bisecting plane. Along withthis, there is a fear in that a constant velocity characteristic andtransmission efficiency are reduced, and strength of the cage is alsosignificantly reduced.

(3) Focus and Inspections

Based on the result of consideration described above, a focus is givento a fixed type constant velocity universal joint of a cross trackgroove type that is excellent in balance of forces applied from balls toa cage. In the fixed type constant velocity universal joint of the crosstrack groove type, track grooves of an outer joint member each includean arc-shaped portion having a curvature center that has no offset in anaxial direction, and are inclined in a circumferential direction withrespect to an axis of the joint. Further, the track grooves are formedwith such inclination directions that the track grooves adjacent to eachother are inclined in opposite directions. A raceway center line of eachtrack groove of an inner joint member is mirror-symmetric with a racewaycenter line of the track groove of the outer joint member. The balls arearranged at intersecting portions between the track grooves of the outerjoint member and the track grooves of the inner joint member.

In the fixed type constant velocity universal joint of the cross trackgroove type, when torque is applied in a range of the normal operatingangle having a small angle and a range of from a medium angle to a largeangle in which the balls are brought into a contact state with respectto the track grooves, owing to the structure in which the ballsbasically generate forces to push the cage in opposite directions in theadjacent track grooves, the moment and the forces applied to the cage bythe balls are balanced. In the range of from the medium angle to thelarge angle, there are variations in magnitude of contact forces betweeneach ball and the track groove of the outer joint member and betweeneach ball and the track groove of the inner joint member. However, ascompared to the related-art axial track offset type, the moment and theforces applied to the cage by the balls are balanced, and hence the cageis stable near the bisecting plane. Moreover, it has been found that,even at the large operating angle at which the ball loses a contact withthe track groove of the outer joint member, as compared to therelated-art axial track offset type, the moment and the forces appliedto the cage by the balls still act so as to be balanced, and hence thecage is not significantly displaced from the bisecting plane.

Based on the results of inspections described above, a conclusion isdrawn as follows. In the fixed type constant velocity universal joint ofthe cross track groove type, even under a state in which the ball losesa contact with the track groove of the outer joint member, the cage isnot significantly displaced from the bisecting plane, thereby beingcapable of minimizing reduction in constant velocity characteristic andtransmission efficiency, and minimizing changes of internal forces.

(4) Novel Ideas

The inventors of the present invention have arrived at an idea of usingthe fixed type constant velocity universal joint of the cross trackgroove type as a base to adopt as the fixed type constant velocityuniversal joint having the maximum operating angle set to be larger thanthe hitherto-adopted operating angle (50°) and having the operation modein which, when the large operating angle is taken, the ball loses acontact at the phase angle (around the phase angle of 0°) at which theball projects from the outer joint member. After the arrival at theidea, as a result of extensive studies, the inventors of the presentinvention hit on an idea of preventing the ball from being dropped offfrom the cage through suppression of a movement amount by which the ballis pushed out from the cage to a radially outer side under a state inwhich the ball loses a contact in the fixed type constant velocityuniversal joint of the cross track groove type, and further hit on anidea of preventing damage to the opening-side end portion of the outerjoint member through suppression of increase in internal forces when theball returns to the track groove of the outer joint member, therebyachieving the present invention.

As a technical measure to achieve the object described above, accordingto the present invention, there is provided a fixed type constantvelocity universal joint, comprising: an outer joint member, which has aplurality of track grooves being formed in a spherical inner peripheralsurface of the outer joint member and extending substantially in anaxial direction, and has an opening side and a back side apart from eachother in the axial direction; an inner joint member, which has aplurality of track grooves being formed in a spherical outer peripheralsurface of the inner joint member and extending substantially in theaxial direction so as to be opposed to the track grooves of the outerjoint member; torque transmission balls incorporated in pairs of thetrack grooves opposed to each other; and a cage configured to retain thetorque transmission balls in pockets, the cage comprising: a sphericalouter peripheral surface to be guided by the spherical inner peripheralsurface of the outer joint member; and a spherical inner peripheralsurface to be guided by the spherical outer peripheral surface of theinner joint member, wherein a raceway center line X of the track grooveof the outer joint member comprises at least an arc-shaped portionhaving a curvature center that has no offset with respect to a jointcenter O in the axial direction, wherein a plane M including the racewaycenter line X and the joint center O is inclined with respect to an axisN-N of the joint, and the track groove is formed with such aninclination direction of the plane M that the track grooves adjacent toeach other in a circumferential direction are inclined in oppositedirections, wherein a raceway center line Y of the track groove of theinner joint member is formed so as to be mirror-symmetric with theraceway center line X of the paired track groove of the outer jointmember with a plane P including the joint center O and being orthogonalto the axis N-N of the joint in a state of an operating angle of 0° as areference, and wherein, when a large operating angle is taken, anoperating angle θ2 at which the torque transmission ball loses a contactwith the track groove of the inner joint member is larger than anoperating angle θ1 at which the torque transmission ball loses a contactwith the track groove of the outer joint member.

With the configuration described above, in the fixed type constantvelocity universal joint having the maximum operating angle set to belarger than the hitherto-adopted operating angle (50°), and having theoperation mode in which, when the large operating angle is taken, theball loses a contact at the phase angle (around the phase angle of 0°)at which the ball projects from the outer joint member, the fixed typeconstant velocity universal joint capable of securing a constantvelocity characteristic, transmission efficiency, and durability can beachieved.

Specifically, it is preferred that the raceway center line X of thetrack groove of the outer joint member described above comprise thearc-shaped portion having the curvature center that has no offset withrespect to the joint center O in the axial direction, and a portiondifferent in shape from the arc-shaped portion. It is preferred that thearc-shaped portion and the portion different in shape from thearc-shaped portion be smoothly connected to each other at a connectionpoint A. It is preferred that the connection point A be located more onthe opening side of the outer joint member than the joint center O. Withthis, a constant velocity characteristic, transmission efficiency, anddurability can be secured. In addition, a length of a track groove thatis effective in keeping a contact, and a size of a wedge angle at thetime of a large operating angle can be adjusted.

When the portion different in shape described above is linear, aneffective track length can be increased.

It is preferred that the operating angle θ2 at which the torquetransmission ball loses a contact with the track groove of the innerjoint member be larger, by 3° or more, than the operating angle θ1 atwhich the torque transmission ball loses a contact with the track grooveof the outer joint member. With this, while the inner joint member isreduced in weight and size, a load of the ball can be borne on the trackgroove of the inner joint member when the ball returns to the trackgroove of the outer joint member. Accordingly, without increasing theinternal forces, damage to the opening-side end portion of the outerjoint member can be prevented, thereby being capable of improvingstrength and durability.

It is preferred that an upper limit of the operating angle θ2 at whichthe torque transmission ball loses a contact with the track groove ofthe inner joint member be set to a value enabling the torquetransmission ball to keep a contact with the pocket of the cage. Withthis, the balls are reliably retained in the pockets of the cage,thereby being capable of preventing generation of noise.

When the number of the torque transmission balls described above is setto be equal to or larger than eight, high efficiency and reduction inweight and size can be achieved.

EFFECTS OF THE INVENTION

According to the present invention, it is possible to achieve the fixedtype constant velocity universal joint, which has the maximum operatingangle set to be larger than the hitherto-adopted operating angle (50°),has the operation mode in which, when a large operating angle is taken,the ball loses a contact in a range of a phase (phase angle of 0°) atwhich the ball projects from the outer joint member, and is capable ofsecuring a constant velocity characteristic, transmission efficiency,and durability.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1a is a longitudinal sectional view for illustrating a fixed typeconstant velocity universal joint according to one embodiment of thepresent invention.

FIG. 1b is a right-side view of FIG. 1 a.

FIG. 2a is a longitudinal sectional view for illustrating an outer jointmember of FIG. 1 a.

FIG. 2b is a right-side view of FIG. 2 a.

FIG. 3a is a front view for illustrating an inner joint member of FIG. 1a.

FIG. 3b is a right-side view of FIG. 3 a.

FIG. 4 is an enlarged transverse sectional view for illustrating onetorque transmission ball and track grooves taken along the line P-P ofFIG. 1 a.

FIG. 5 is a view for illustrating comparison between a longitudinalcross section of the fixed type constant velocity universal joint ofFIG. 1a and a longitudinal cross section of a fixed type constantvelocity universal joint of a cross track groove type having thehitherto-adopted maximum operating angle.

FIG. 6a is a longitudinal sectional view for illustrating the fixed typeconstant velocity universal joint of FIG. 1a and FIG. 1b when the fixedtype constant velocity universal joint takes the maximum operatingangle.

FIG. 6b is a right-side view of FIG. 6 a.

FIG. 7 is an enlarged longitudinal sectional view for illustrating theportion E of FIG. 6 a.

FIG. 8 is an illustration in which a range in which the torquetransmission ball loses a contact with the track groove of the outerjoint member at the maximum operating angle is illustrated on FIG. 1 b.

FIG. 9 is a development view of an inner peripheral surface of the outerjoint member, for illustrating a difference given by inclinationdirections of the track grooves between ranges in which the torquetransmission balls lose contacts with the track grooves of the outerjoint member of FIG. 8.

FIG. 10a is a longitudinal sectional view for illustrating a state inwhich the torque transmission ball loses a contact with the track grooveof the outer joint member when the fixed type constant velocityuniversal joint of FIG. 1a and FIG. 1b takes a large operating angle.

FIG. 10b is a right-side view of FIG. 10 a.

FIG. 11 is a development view of the inner peripheral surface of theouter joint member, for illustrating a state in which the torquetransmission ball loses a contact with the track groove of the outerjoint member of FIGS. 10.

FIG. 12 is an enlarged longitudinal sectional view for illustrating theportion F of FIG. 10 a.

FIG. 13a is a longitudinal sectional view for illustrating a state inwhich the torque transmission ball loses a contact with the track grooveof the inner joint member when the fixed type constant velocityuniversal joint of FIG. 1a and FIG. 1b takes a large operating angle.

FIG. 13b is a right-side view of FIG. 13 a.

FIG. 14 is a development view of the inner peripheral surface of theouter joint member, for illustrating a positional relationship among thetrack grooves of the outer joint member and the torque transmissionballs when the operating angle illustrated in FIG. 13a and FIG. 13b istaken.

FIG. 15 is an enlarged longitudinal sectional view for illustrating theportion H of FIG. 13 a.

EMBODIMENTS OF THE INVENTION

A fixed type constant velocity universal joint according to oneembodiment of the present invention is described with reference to FIGS.1 to FIG. 15. FIG. 1a is a longitudinal sectional view for illustratingthe fixed type constant velocity universal joint according to oneembodiment of the present invention. FIG. 1b is a right-side view ofFIG. 1a . FIG. 2a is a longitudinal sectional view for illustrating theouter joint member of FIG. 1 a. FIG. 2b is a right-side view of FIG. 2a. FIG. 3a is a front view for illustrating an inner joint member of FIG.1 a. FIG. 3b is a right-side view of FIG. 3a . As illustrated in FIG. 1aand FIG. 1b , a fixed type constant velocity universal joint 1 accordingto this embodiment is of a cross track groove type and mainly comprisesan outer joint member 2, an inner joint member 3, toque transmissionballs 4 (hereinafter simply referred to as “balls”), and a cage 5. Aspherical inner peripheral surface 6 of the outer joint member 2 haseight track grooves 7. A spherical outer peripheral surface 8 of theinner joint member 3 has eight track grooves 9 opposed to the trackgrooves 7 of the outer joint member 2. The cage 5 configured to retainthe balls 4 is arranged between the spherical inner peripheral surface 6of the outer joint member 2 and the spherical outer peripheral surface 8of the inner joint member 3. A spherical outer peripheral surface 12 ofthe cage 5 is fitted to the spherical inner peripheral surface 6 of theouter joint member 2 in a freely slidable manner, and a spherical innerperipheral surface 13 of the cage 5 is fitted to the spherical outerperipheral surface 8 of the inner joint member 3 in a freely slidablemanner.

A curvature center of the spherical inner peripheral surface 6 of theouter joint member 2 and the curvature center of the spherical outerperipheral surface 8 of the inner joint member 3 are each formed at ajoint center 0. The curvature centers of the spherical outer peripheralsurface 12 and the spherical inner peripheral surface 13 of the cage 5which are fitted to the spherical inner peripheral surface 6 of theouter joint member 2 and the spherical outer peripheral surface 8 of theinner joint member 3, respectively, are also located at the joint centerO.

A radially inner hole 10 of the inner joint member 3 has a female spline(the spline includes a serration, which similarly applies in thefollowing description) 11, and a male spline 15 formed at an end portionof an intermediate shaft 14 (see FIG. 6a ) is fitted to the femalespline 11, thereby coupling the intermediate shaft 14 to the inner jointmember 3 so as to enable transmission of torque. The inner joint member3 and the intermediate shaft 14 are positioned in an axial direction bya stopper ring 16.

As illustrated in FIG. 1a , FIG. 1b , FIG. 2a , FIG. 2b , FIG. 3a , andFIG. 3b , the eight track grooves 7 and 9 of the outer joint member 2and the inner joint member 3 extend substantially in the axialdirection. With respect to an axis N-N of the joint, the track grooves 7and 9 are formed with such inclination directions that track grooves 7Aand 7B adjacent to each other in the circumferential direction areinclined in opposite directions and that the track grooves 9A and 9Badjacent to each other in the circumferential direction are inclined inopposite directions. The eight balls 4 are arranged at respectiveintersecting portions of paired track grooves 7A and 9A and paired trackgrooves 7B and 9B of the outer joint member 2 and the inner joint member3. In FIG. 1a , illustration is given of the track grooves 7 and 9 in astate in which respective cross sections taken along the plane Millustrated in FIG. 2a and the plane Q illustrated in FIG. 3a arerotated to an inclination angle γ=0°. Under a state of taking anoperating angle O, the axis N-N of the joint serves also as an axisNo-No of the outer joint member and an axis Ni-Ni of the inner jointmember.

With reference to FIG. 1a , the fixed type constant velocity universaljoint according to this embodiment is described as an example of aconfiguration described in Claims in which “the raceway center line (X)of the track groove of the outer joint member comprises an arc-shapedportion having a curvature center that has no offset with respect to thejoint center (O) in the axial direction, and a portion different inshape from the arc-shaped portion, in which the portion different inshape from the arc-shaped portion is smoothly connected to thearc-shaped portion at a connection point (J), and in which theconnection point (J) is located more on the opening side of the outerjoint member than the joint center (O)”. The above-mentioned racewaycenter line X of the track groove of the outer joint member comprisesthe arc-shaped portion having the curvature center that has no offsetwith respect to the joint center O in the axial direction, and theportion different in shape from the arc-shaped portion. With thisconfiguration, a constant velocity characteristic, transmissionefficiency, and durability can be secured. In addition, a length of atrack groove that is effective in keeping a contact, and a size of awedge angle at the time of a large operating angle can be adjusted.

As illustrated in FIG. 1a , the track groove 7 of the outer joint member2 has the raceway center line X. The track groove 7 is formed of a firsttrack groove portion 7 a and a second track groove portion 7 b. Thefirst track groove portion 7 a has an arc-shaped raceway center line Xahaving a curvature center at the joint center O. The second track grooveportion 7 b has a linear raceway center line Xb. The raceway center lineXb of the second track groove portion 7 b is smoothly connected as atangent to the raceway center line Xa of the first track groove portion7 a. The linear portion described above is the portion different inshape from the arc-shaped portion mentioned above. The raceway centerline Xa of the first track groove portion 7 a corresponds to “thearc-shaped portion having the curvature center that has no offset withrespect to the joint center (O) in the axial direction”, and the racewaycenter line X of the track groove of the outer joint member inDescription and Claims comprises at least the above-mentioned arc-shapedportion.

In order to accurately indicate a mode and a shape of each track grooveextending substantially in the axial direction, description is made withuse of the term “raceway center line” in Description. Here, the racewaycenter line corresponds to a locus formed by a center of the ball whenthe ball arranged in the track groove moves along the track groove.

As illustrated in FIG. 1a , the track groove 9 of the inner joint member3 has a raceway center line Y. The track groove 9 is formed of a firsttrack groove portion 9 a and a second track groove portion 9 b. Thefirst track groove portion 9 a has an arc-shaped raceway center line Yahaving a curvature center at the joint center O. The second track grooveportion 9 b has a linear raceway center line Yb. The raceway center lineYb of the second track groove portion 9 b is smoothly connected as atangent to the raceway center line Ya of the first track groove portion9 a. Respective curvature centers of the raceway center lines Xa and Yaof the first track groove portions 7 a and 9 a of the outer joint member2 and the inner joint member 3 are arranged at the joint center O, thatis, on the axis N-N of the joint. As a result, the depths of the trackgrooves can be uniformly set, and processing can easily be carried out.

With reference to FIG. 2a and FIG. 2b , a detailed description is madeof the state in which the track grooves 7 of the outer joint member 2are inclined in the circumferential direction with respect to the axisN-N of the joint. The track grooves 7 of the outer joint member 2 aredenoted by reference symbols 7A and 7B based on the difference in theinclination directions. As illustrated in FIG. 2a , a plane M includingthe raceway center line X of the track groove 7A and the joint center Ois inclined by the angle y with respect to the axis N-N of the joint.Regarding each of the track grooves 7B adjacent to the track groove 7Ain the circumferential direction, although illustration is omitted, theplane M including the raceway center line X of the track groove 7B andthe joint center 0 is inclined by the angle y with respect to the axisN-N of the joint in the direction opposite to the inclination directionof the track groove 7A.

In this embodiment, the entirety of the raceway center line X of thetrack groove 7A, that is, both of the raceway center line Xa of thefirst track groove portion 7 a and the raceway center line Xb of thesecond track groove portion 7 b are formed on the plane M.

Here, a supplementary description is made of reference symbols of thetrack grooves. The entire track groove of the outer joint member 2 isdenoted by reference symbol 7. The first track groove portion of thetrack groove is denoted by reference symbol 7 a, and the second trackgroove portion is denoted by reference symbol 7 b. Further, trackgrooves having different inclination directions are denoted by referencesymbols 7A and 7B for distinction. Respective first track grooveportions are denoted by reference symbols 7Aa and 7Ba, and respectivesecond track groove portions are denoted by reference symbols 7Ab and7Bb. The track grooves of the inner joint member 3 to be described laterare denoted by reference symbols in a similar manner.

Next, with reference to FIG. 3a and FIG. 3b , a detailed description ismade of the state in which the track grooves 9 of the inner joint member3 are inclined in the circumferential direction with respect to the axisN-N of the joint. The track grooves 9 of the inner joint member 3 aredenoted by reference symbols 9A and 9B based on the difference in theinclination directions. As illustrated in FIG. 3a , a plane Q includingthe raceway center line Y of the track groove 9A and the joint center Ois inclined by the angle y with respect to the axis N-N of the joint.Regarding each of the track grooves 9B adjacent to the track groove 9Ain the circumferential direction, although illustration is omitted, theplane Q including the raceway center line Y of the track groove 9B andthe joint center O is inclined by the angle γ with respect to the axisN-N of the joint in the direction opposite to the inclination directionof the track groove 9A. It is preferred that the inclination angle y beset within the range of from 4° to 12° in consideration of theoperability of the fixed type constant velocity universal joint 1 and aspherical surface width I on the side on which the track grooves of theinner joint member 3 are closest to each other.

Moreover, similarly to the outer joint member 2 mentioned above, in thisembodiment, the entirety of the raceway center line Y of the trackgroove 9A, that is, both of the raceway center line Ya of the firsttrack groove portion 9 a and the raceway center line Yb of the secondtrack groove portion 9 b are formed on the plane Q. The raceway centerline Y of the track groove 9 of the inner joint member 3 is formed so asto be mirror-symmetric with the raceway center line X of the pairedtrack groove 7 of the outer joint member 2 with the plane P includingthe joint center O and being orthogonal to the axis N-N of the joint inthe state of the operating angle of 0° as a reference.

With reference to FIG. 1a , a detailed description is made of the trackgrooves of the outer joint member 2 and the inner joint member 3 as seenon the longitudinal cross section. In FIG. 1a , as mentioned above,illustration is given of the track grooves 7 and 9 in the state in whichrespective cross sections as seen on the plane M illustrated in FIG. 2aand the plane Q illustrated in FIG. 3a are rotated to the inclinationangle γ=0°. That is, with regard to the outer joint member 2, FIG. 2a isa sectional view taken along the plane M of FIG. 2a including theraceway center line X of the track groove 7A of the outer joint member 2and the joint center O. Thus, in a strict sense, FIG. 1a is not alongitudinal sectional view taken along the plane including the axis N-Nof the joint and is an illustration of the cross section inclined by theangle γ. In FIG. 1a , the track groove 7A of the outer joint member 2 isillustrated. The track groove 7B has the inclination direction oppositeto that of the track groove 7A, and other configurations of the trackgroove 7B are the same as those of the track groove 7A. Therefore,description of the track groove 7B is omitted. The spherical innerperipheral surface 6 of the outer joint member 2 has the track grooves7A extending substantially along the axial direction.

The track groove 7A has the raceway center line X. The track groove 7Ais formed of the first track groove portion 7Aa and the second trackgroove portion 7Ab. The first track groove portion 7Aa has thearc-shaped raceway center line Xa having a curvature center at the jointcenter O (no offset in the axial direction). The second track grooveportion 7Ab has the linear raceway center line Xb. At an end portion Jof the raceway center line Xa of the first track groove portion 7Aa onthe opening side, the linear raceway center line Xb of the second trackgroove portion 7Ab is smoothly connected as a tangent. That is, the endportion J serves as a connection point between the first track grooveportion 7Aa and the second track groove portion 7Ab. The end portion Jis located more on the opening side than the joint center O. Therefore,the linear raceway center line Xb of the second track groove portion 7Abconnected as a tangent at the end portion J of the raceway center lineXa of the first track groove portion 7Aa on the opening side is formedin such a manner as to approach the axis N-N of the joint as approachingthe opening side. With this configuration, the length of the track thatis effective can be increased, and the wedge angle can be prevented frombeing excessively large.

As illustrated in FIG. 1a , a straight line connecting the end portion Jand the joint center O to each other is denoted by reference symbol S.An axis N′-N′ of the joint projected on the plane M including theraceway center line X of the track groove 7A and the joint center O isinclined by the angle y with respect to the axis N-N of the joint, andan angle formed between a perpendicular line K, which is perpendicularto the axis N′-N′ at the joint center O, and the straight line S isdenoted by reference symbol β′. The perpendicular line K described aboveis located on the plane P including the joint center O and beingorthogonal to the axis N-N of the joint in the state of the operatingangle of 0°. Thus, an angle β formed by the straight line S with respectto the plane P in the present invention has a relationship ofsinβ=sinβ′×cosγ.

Similarly, with reference to FIG. 1a , a detailed description is made ofthe track grooves of the inner joint member 3 as seen on thelongitudinal cross section. FIG. 1a is a sectional view taken along theplane Q of FIG. 3a including the raceway center line Y of the trackgroove 9A of the inner joint member 3 and the joint center O. Thus, in astrict sense, FIG. 1a is not a longitudinal sectional view taken alongthe plane including the axis N-N of the joint and is an illustration ofthe cross section inclined by the angle y. In FIG. 1a , the track groove9A of the inner joint member 3 is illustrated. The track groove 9B hasthe inclination direction opposite to that of the track groove 9A, andother configurations of the track groove 9B are the same as those of thetrack groove 9A. Therefore, description of the track groove 9B isomitted. The spherical outer peripheral surface 8 of the inner jointmember 3 has the track grooves 9A extending substantially along theaxial direction.

The track groove 9A has the raceway center line Y. The track groove 9Ais formed of a first track groove portion 9Aa and a second track grooveportion 9Ab. The first track groove portion 9Aa has the arc-shapedraceway center line Ya having a curvature center at the joint center O(no offset in the axial direction). The second track groove portion 9Abhas the linear raceway center line Yb. At an end portion J′ of theraceway center line Ya of the first track groove portion 9Aa on the backside, the raceway center line Yb of the second track groove portion 9Abis smoothly connected as a tangent. That is, the end portion J′ servesas a connection point between the first track groove portion 9Aa and thesecond track groove portion 9Ab. The end portion J′ is located more onthe back side than the joint center O. Therefore, the linear racewaycenter line Yb of the second track groove portion 9Ab connected as atangent at the end portion J′ of the raceway center line Ya of the firsttrack groove portion 9Aa on the back side is formed in such a manner asto approach the axis N-N of the joint as approaching the back side. Withthis configuration, the length of the track that is effective can beincreased, and the wedge angle can be prevented from being excessivelylarge.

As illustrated in FIG. 1a , a straight line connecting the end portionJ′ and the joint center O to each other is denoted by reference symbolS′. The axis N′-N′ of the joint projected on the plane Q including theraceway center line Y of the track groove 9A and the joint center O isinclined by the angle y with respect to the axis N-N of the joint, andan angle formed between the perpendicular line K, which is perpendicularto the axis N′-N′ at the joint center O, and the straight line S′ isdenoted by reference symbol β′. The perpendicular line K described aboveis located on the plane P including the joint center O and beingorthogonal to the axis N-N of the joint in the state of the operatingangle of 0°. Thus, an angle β formed by the straight line S′ withrespect to the plane P including the joint center O in the state of theoperating angle of 0° has a relationship of sinβ=sinβ′×cosγ.

Next, description is made of the angle β formed by each of the straightlines S and S′ with respect to the plane P including the joint center Oin the state of the operation angle of 0° and being orthogonal to theaxis N-N of the joint. When the operating angle θ is taken, the ball 4moves by θ/2 with respect to the plane P including the joint center O ofthe outer joint member 2 and the inner joint member 3. The angle β isdetermined based on ½ of the operating angle that is frequently used,and the range of the track groove with which the ball 4 comes intocontact is determined within the range of the operating angle that isfrequently used. Here, a definition of the normal operating angle thatis frequently used is given. A normal operating angle of a joint is anoperating angle that is formed in a fixed type constant velocityuniversal joint for a front drive shaft when an automobile with onepassenger is steered to go straight on a horizontal and flat road. Ingeneral, the normal operating angle is selected and determined withinthe range of from 2° to 15° depending on design conditions for varioustypes of automobiles.

With the angle β described above, in FIG. 1a , the end portion J of theraceway center line Xa of the first track groove portion 7Aa correspondsto a center position of the ball that moves most toward the opening sidealong the axial direction at the time of the normal operating angle.Similarly, in the inner joint member 3, the end portion J′ of theraceway center line Ya of the first track groove portion 9Aa correspondsto a center position of the ball that moves most toward the back sidealong the axial direction at the time of the normal operating angle.With such settings, within the range of the normal operating angle, theballs 4 are located at the first track groove portions 7Aa and 9Aa andthe first track groove portions 7Ba and 9Ba, which have the oppositeinclination direction, of the outer joint member 2 and the inner jointmember 3. Therefore, forces acting in opposite directions are applied bythe balls 4 to the pockets 5 a of the cage 5 adjacent to each other inthe circumferential direction, thereby stabilizing the cage 5 at theposition of the joint center O (see FIG. 1a ). Therefore, a contactforce between the spherical outer peripheral surface 12 of the cage 5and the spherical inner peripheral surface 6 of the outer joint member 2and a contact force between the spherical inner peripheral surface 13 ofthe cage 5 and the spherical outer peripheral surface 8 of the innerjoint member 3 are suppressed, and torque loss and generation of heatare suppressed, thereby improving the durability.

In the range of the large operating angle, the balls 4 arranged in thecircumferential direction are temporarily and separately located at thefirst track groove portions 7Aa and 9Aa and the second track grooveportions 7Ab and 9Ab. As a result, the contact forces are generated atthe spherical-surface contact portions 12 and 6 between the cage 5 andthe outer joint member 2 and at the spherical-surface contact portions13 and 8 between the cage 5 and the inner joint member 3. However, ascompared to a related-art axial track offset type, a moment and theforces applied to the cage 5 by the balls 4 are balanced, and hence thecage 5 is stable near a bisecting plane. Further, the range of the largeoperating angle is not frequently used, and the fixed type constantvelocity universal joint 1 according to this embodiment is thus capableof suppressing the torque loss and generation of heat as a whole.Accordingly, a fixed type constant velocity universal joint which issmall in torque loss and generation of heat and is highly efficient canbe achieved.

FIG. 4 is an enlarged transverse sectional view for illustrating oneball and track grooves taken along the line P-P of FIG. 1a . In FIG. 4,illustration is given of the track grooves 7 and 9 in a state in whichrespective cross sections taken along the plane M illustrated in FIG. 2aand the plane Q illustrated in FIG. 3a are rotated to an inclinationangle γ=0°. A transverse sectional shape of each of the track grooves 7of the outer joint member 2 and the track grooves 9 of the inner jointmember 3 is an elliptical shape or a gothic-arch shape. As illustratedin FIG. 4, the ball 4 is brought into angular contact with the trackgroove 7 of the outer joint member 2 at two points C1 and C2 and isbrought into angular contact with the track groove 9 of the inner jointmember 3 at two points C3 and C4. It is preferred that an angle (contactangle a) formed between a straight line passing through a center Ob ofthe ball 4 and each of the contacts C1, C2, C3 and C4 and a straightline passing through the center Ob of the ball 4 and the joint center O(see FIG. 1a ) be set to be equal to or larger than 30°. The transversesectional shape of each of the track grooves 7 and 9 may be an arcshape, and the track grooves 7 and 9 and the balls 4 may be brought intocircular contact with each other.

The overall configuration of the fixed type constant velocity universaljoint 1 according to this embodiment is as described above. The fixedtype constant velocity universal joint 1 according to this embodiment isset to have a maximum operating angle that significantly exceeds 50°.The characteristic configurations are as described below.

(1) In a fixed type constant velocity universal joint of a cross trackgroove type, there is achieved an operation mode in which the ball losesa contact when the maximum operating angle is taken.

(2) In addition, when a large operating angle is taken, an operatingangle θ2 at which the ball 4 loses a contact with the track groove 9 ofthe inner joint member 3 is set to be larger than an operating angle θ1at which the ball 4 loses a contact with the track groove 7 of the outerjoint member 2.

With the configurations described above, the fixed type constantvelocity universal joint of the cross track groove type has theoperation mode in which, when the maximum operating angle is taken, theball loses a contact. Thus, even at the large operating angle at whichthe ball 4 loses a contact with the track groove 7 of the outer jointmember 2, the moment and the forces applied to the cage 5 by the balls 4act so as to be balanced, and hence the cage 5 is not significantlydisplaced from the bisecting plane. The characteristic configuration (2)described above is combined with the advantageous characteristicconfiguration (1) that is basically provided to the fixed type constantvelocity universal joint of the cross track groove type and is capableof minimizing reduction in constant velocity characteristic andtransmission efficiency, and minimizing changes of internal forces.Through the combination of the configurations, the fixed type constantvelocity universal joint, which has the maximum operating angle set tobe larger than the hitherto-adopted operating angle (50°) and has theoperation mode in which the ball loses a contact, can be dramaticallyimproved in constant velocity characteristic, transmission efficiency,changes of internal forces, strength, and durability.

First, the characteristic configuration (1) of the fixed type constantvelocity universal joint 1 according to this embodiment is describedwith reference to FIG. 5. An upper half of FIG. 5 with respect to acenter line (axis of the joint) is a longitudinal sectional view forillustrating the fixed type constant velocity universal joint 1according to this embodiment, and a lower half of FIG. 5 is alongitudinal sectional view for illustrating the fixed type constantvelocity universal joint of the cross track groove type having thehitherto-adopted maximum operating angle and comprising eight balls. Afixed type constant velocity universal joint 101 of the cross trackgroove type illustrated in the lower half of FIG. 5 has thehitherto-adopted maximum operating angle, that is, has the maximumoperating angle of 47°. The fixed type constant velocity universal joint101 mainly comprises an outer joint member 102, an inner joint member103, balls 104, and a cage 105. Track grooves 107 of the outer jointmember 102 and track grooves 109 of the inner joint member 103 of thefixed type constant velocity universal joint 101 are the same as thetrack grooves 7 and 9 in this embodiment, and hence only outlinesthereof are described.

The track grooves 107 of the outer joint member 102 of the fixed typeconstant velocity universal joint 101 are each formed of a first trackgroove portion 107 a and a second track groove portion 107 b, and thetrack grooves 109 of the inner joint member 103 of the fixed typeconstant velocity universal joint 101 are each formed of a first trackgroove portion 109 a and a second track groove portion 109 b. The firsttrack groove portions 107 a and 109 a respectively have arc-shapedraceway center lines xa and ya each having a curvature center at thejoint center O (no offset in the axial direction), and the second trackgroove portions 107 b and 109 b respectively have linear raceway centerlines xb and yb. The raceway center line xa of the first track grooveportion 107 a and the raceway center line xb of the second track grooveportion 107 b of the outer joint member 102 are tangentially andsmoothly connected to each other at a connection point A that is more onthe opening side than the joint center O. The raceway center line ya ofthe first track groove portion 109 a and the raceway center line yb ofthe second track groove portion 109 b of the inner joint member 103 aretangentially and smoothly connected to each other at a connection pointA′ on a back side.

Similarly to the fixed type constant velocity universal joint 1according to this embodiment, the track grooves 107 of the outer jointmember 102 and the track grooves 109 of the inner joint member 103 areinclined in the circumferential direction with respect to the axis N-Nof the joint, and are formed with such inclination directions that thetrack grooves 107 adjacent to each other in the circumferentialdirection are inclined in opposite directions and that the track grooves109 adjacent to each other in the circumferential direction are inclinedin opposite directions. A straight line L or L′ connecting theconnection point A or A′ and the joint center O to each other forms anangle β₁ with respect to the plane P including the joint center O andbeing orthogonal to the axis N-N of the joint . The angle β₁ is set tobe larger than the angle β of the fixed type constant velocity universaljoint 1 according to this embodiment.

The fixed type constant velocity universal joint 101 has an operationmode in which the balls 104 are always kept in a contact state withrespect to the track grooves 107 of the outer joint member 102 up to themaximum operating angle (47°). An inlet chamfer 120 formed at anopening-side end portion of the outer joint member 102 is set such that,at the maximum operating angle, an intermediate shaft does not interferewith the inlet chamfer 120 and that a contact state between the balls104 and the track grooves 107 of the outer joint member 102 is kept.Accordingly, an axial dimension L2 from the joint center O to anopening-side end surface of the outer joint member 102 is set to berelatively long.

When a large operating angle with the maximum operating angle largerthan 47° is required, the intermediate shaft interferes with the inletchamfer 120. In order to avoid the interference, the inlet chamfer 120is moved in the axial direction toward the joint center O, and aninclination angle is suitably increased. However, along with this, it isrequired that the axial dimension from the joint center O to theopening-side end surface of the outer joint member 102 be reduced. Thefixed type constant velocity universal joint 1 according to thisembodiment meets this requirement, and the maximum operating angle ofthe fixed type constant velocity universal joint 1 is set to besignificantly larger than the hitherto-adopted maximum operating angle.In the fixed type constant velocity universal joint 1 according to thisembodiment illustrated in the upper half of FIG. 5, an axial dimensionL1 from the joint center O to an opening-side end surface of the outerjoint member 2 is smaller than the axial dimension L2 from the jointcenter O to an opening-side end surface of the outer joint member 102 ofthe fixed type constant velocity universal joint 101 having thehitherto-adopted maximum operating angle, which is illustrated in thelower half of FIG. 5.

With reference to FIG. 6a and FIG. 6b , description is made of a statein which the fixed type constant velocity universal joint 1 according tothis embodiment takes the maximum operating angle. FIG. 6a is alongitudinal sectional view for illustrating the fixed type constantvelocity universal joint 1 when the fixed type constant velocityuniversal joint 1 takes the maximum operating angle. FIG. 6b is aright-side view of FIG. 6a . As described above, a length of each of thetrack grooves 7 on the opening side of the outer joint member 2 isreduced. Accordingly, in the operation mode of the fixed type constantvelocity universal joint 1 according to this embodiment, as illustratedin FIG. 6a , when a maximum operating angle θmax significantly largerthan the hitherto-adopted maximum operating angle is taken, the ball 4comes off an opening-side end portion of the track groove 7 of the outerjoint member 2 and loses a contact with the track groove 7. Further, theball 4 comes off a back-side end portion of the track groove 9 of theinner joint member 3 and loses a contact with the track groove 9. Asillustrated in FIG. 6b , when the maximum operating angle θmax is taken,the center Ob of the ball 4 is most distant from the opening-side endportion of the track groove 7 of the outer joint member 2 at a positionof a phase angle φ0.

FIG. 6a is an illustration of a state in which the axis Ni-Ni of theinner joint member 3 (intermediate shaft 14) is bent with respect to theaxis No-No of the outer joint member 2 to the maximum operating angleθmax (for example, 55°) on the drawing sheet of FIG. 6a . An axis Nc-Ncof the cage 5 is inclined at a bisecting angle θmax/2. As illustrated inFIG. 6b , an illustration of the center Ob of the uppermost ball 4 isslightly displaced in the circumferential direction from the phase angleof 0° due to a relationship with the inclination angle γ of the trackgroove 7 of the outer joint member 2. Here, the phase angle of 0° refersto an angular position of the center Ob of the uppermost (top) ball 4 inthe circumferential direction under a state in which the operating angleis 0° as illustrated in FIG. 1b . In Description and Claims, the phaseangle is indicated as proceeding in a counterclockwise direction fromthe phase angle of 0° (the phase angle of 0° is indicated by “φ0” inFIG. 6b , and hereinafter also referred to as “φ0”). Further, inDescription and Claims, the term “maximum operating angle θmax” is usedwith the meaning of a maximum operating angle that is allowed when thefixed type constant velocity universal joint 1 is used.

FIG. 6a is an illustration of a state in which the intermediate shaft 14is in abutment against the inlet chamfer 20 at the time of the maximumoperating angle. However, in actuality, the inlet chamfer 20 is set soas to have such a shape and a dimension that a slight margin is givenwith respect to a radially outer surface of the intermediate shaft 14when the maximum operating angle is taken. The inlet chamfer 20functions as a stopper surface for a case in which the intermediateshaft 14 exceeds the maximum operating angle.

As illustrated in FIG. 6a , in the fixed type constant velocityuniversal joint 1 according to this embodiment, when the maximumoperating angle is taken, the ball 4, which is located around the phaseangle φ0 and moves toward the opening side of the track groove 7 of theouter joint member 2, comes off the opening-side end portion of thetrack groove 7 of the outer joint member 2 (inlet chamfer 20) and losesa contact with the track groove 7. Further, the ball 4 comes off theback-side end portion of the track groove 9 of the inner joint member 3and loses a contact with the track groove 9. This state is described indetail with reference to FIG. 7 for illustrating the portion E of FIG.6a in an enlarged manner.

A surface position 4 ao of the ball 4 when the ball 4 comes into contactwith the track groove 7 and the inlet chamfer 20 formed at theopening-side end portion of the outer joint member 2, a surface position4 ai of the ball 4 when the ball 4 comes into contact with the trackgroove 9, and a surface position 4 b of the ball 4 when the ball 4 comesinto contact with the pocket 5 a of the cage 5 are each indicated by abroken line. Further, a contact locus obtained by connecting thecontacts C2 (or C1, see FIG. 4), which are given between the trackgroove 7 of the outer joint member 2 and the ball 4, in the axialdirection is denoted by CLo, and a contact locus obtained by connectingthe contacts C3 (or C4, see FIG. 4), which are given between the trackgroove 9 of the inner joint member 3 and the ball 4, in the axialdirection is denoted by CLi. The contact locus CLo and the contact locusCLi are each indicated by a broken line. The contact loci CLo and CLiare formed at positions apart from the groove bottoms of the trackgrooves 7 and 9, respectively.

The contact locus CLo ends at an edge portion of the inlet chamfer 20 onthe opening side of the outer joint member 2. The edge portion of theinlet chamfer 20 is the opening-side end portion of the track groove 7of the outer joint member 2. The surface position 4 ao of the ball 4 ison a right side in FIG. 7 with respect to the end of the contact locusCLo, and the ball 4 and the track groove 7 are in a non-contact state.The ball 4 that loses a contact with the track groove 7 is one or two ofthe eight balls, and the one or two balls 4 are not involved in torquetransmission. The contact locus CLi of the track groove 9 of the innerjoint member 3 ends at the back-side end portion 3 a. The surfaceposition 4 ai of the ball 4 is on a left side in FIG. 7 with respect tothe end of the contact locus CLi, and the ball 4 and the track groove 9are in a non-contact state. An interval between the surface position 4ao of the ball 4 and the end of the contact locus CLo on the trackgroove 7 of the outer joint member 2 is set to be larger than aninterval between the surface position 4 ai of the ball 4 and the end ofthe contact locus CLi on the track groove 9 of the inner joint member 3.

A contact state between the surface position 4 b of the ball 4 and thepocket 5 a of the cage 5 is kept at a radial position before thespherical outer peripheral surface 12 of the cage 5. The pocket 5 a andthe ball 4 are fitted to each other with an extremely slightinterference margin, and the ball 4 and the track groove 9 of the innerjoint member 3 are in a non-contact state. Thus, no inevitableinterference occurs between the track groove 9 and the ball 4. As aresult, the ball 4 is reliably retained in the pocket 5 a, and forexample, generation of noise is prevented. Even when the ball 4 comesoff the pocket 5 a, a distance W between the edge portion of the inletchamfer 20 of the track groove 7 and an edge portion of the pocket 5 aof the cage 5 is set so as to satisfy a relationship of Db>W with adiameter Db of the ball 4, and hence the ball 4 is prevented from beingdropped off.

Next, a range in which the ball 4 comes off the track groove 7, that is,a phase angle range (hereinafter, also simply referred to as “range”) inwhich the ball 4 and the track groove 7 are brought into a non-contactstate is described with reference to FIG. 8. FIG. 8 is an illustrationin which the range in which the ball 4 comes off the track groove 7 ofthe outer joint member 2 at the maximum operating angle is illustratedon FIG. 1b . In FIG. 8, the range in which the ball 4 comes off thetrack groove 7 of the outer joint member 2 is indicated by the arrows.The leader line of each arrow indicates the center Ob of the ball 4. Inthe fixed type constant velocity universal joint 1 according to thisembodiment, the track grooves 7A and 7B of the outer joint member 2 eachhave the inclination angle y with respect to the axis N-N of the jointin the circumferential direction, and the track grooves 7A and 7B areformed with such inclination directions that the track grooves 7A and 7Badjacent to each other in the circumferential direction are inclined inopposite directions. Accordingly, as illustrated in FIG. 8, a phaseangle range M_(A) in which the ball 4 comes off the track groove 7A isslightly different from a phase angle range M_(B) in which the ball 4comes off the track groove 7B.

A detailed description is made of the range in which the ball 4 comesoff the track groove 7 using one ball 4 located in the track groove 7Ain FIG. 6a , FIG. 6b , and FIG. 8 as an example. Under a state in whichthe axis No-No of the outer joint member 2 and the axis Ni-Ni of theinner joint member 3 (intermediate shaft 14) illustrated in FIG. 6a arefixed, when the fixed type constant velocity universal joint 1 isrotated in the counterclockwise direction from the phase angle φ0, at aposition of a phase angle φ2 _(A) (for example,) φ2 _(A)=336°) beforethe phase angle φ0 in FIG. 8, the ball 4 comes off the opening-side endportion of the track groove 7A of the outer joint member 2, and loses acontact with the track groove 7A to start a non-contact state withrespect to the track groove 7A. When the fixed type constant velocityuniversal joint 1 is rotated beyond the phase angle φ0, at a position ofa phase angle φ1 _(A) (for example, φ1 _(A)=24°) the ball 4 returns tothe opening-side end portion of the track groove 7A of the outer jointmember 2 to start a contact state with respect to the track groove 7A.

In the description above, one ball 4 is described as an example.However, in actuality, when the fixed type constant velocity universaljoint 1 is rotated, the eight balls 4 sequentially pass through thephase angle range in which the balls 4 are brought into the non-contactstate. The ball 4 located in the track groove 7B also has the sameoperation as that of the ball 4 located in the track groove 7A. However,the track groove 7B is formed so as to have the inclination directionopposite to the inclination direction of the track groove 7A.Accordingly, at a phase angle φ2 _(B) (for example, φ2 _(B)=333°), theball 4 comes off the opening-side end portion of the track groove 7B ofthe outer joint member 2, and loses a contact with the track groove 7Bto start a non-contact state with respect to the track groove 7B.Further, at a phase angle φ1 _(B) (for example, φ1 _(B)=27 °), the ball4 returns to the opening-side end portion of the track groove 7B of theouter joint member 2 to start a contact state with respect to the trackgroove 7B. Accordingly, as illustrated in FIG. 8, the range M_(A) inwhich the ball 4 comes off the track groove 7A is slightly differentfrom the range M_(B) in which the ball 4 comes off the track groove 7B.

Moreover, the reason is described with reference to FIG. 9. FIG. 9 is adevelopment view of an inner peripheral surface of the outer jointmember, for illustrating a difference given by inclination directions ofthe track grooves between ranges in which the torque transmission ballslose contacts with the track grooves of the outer joint member of FIG.8. A right side of a center line extending in the up-and-down directionof the drawing sheet of FIG. 9 is an illustration of a state in whichthe ball 4 comes off the track groove 7A, and a left side thereof is anillustration of a state in which the ball 4 comes off the track groove7B. The outline arrow of FIG. 9 indicates a direction of applying torquefrom the inner joint member 3 to the outer joint member 2. The outlinearrow of FIG. 11 or FIG. 14 to be described later similarly indicatesthe torque applying direction.

The track grooves 7 are inclined with respect to the axis. Thus, inaccordance with the torque applying direction indicated in FIG. 9, theball 4 is brought into contact with the track groove 7A at a positiondisplaced toward the back side with respect to the center Ob of the ball4, and the ball 4 is brought into contact with the track groove 7B at aposition displaced toward the opening side with respect to the center Obof the ball 4. Accordingly, the surface position 4 ao of the ball 4arrives at the end of the contact locus CLo of the track groove 7A (edgeportion of the inlet chamfer 20) so that the ball 4 is at the phaseangle φ2 _(A) at which the ball 4 loses a contact. Meanwhile, thesurface position 4 ao of the ball 4 arrives at the end of the contactlocus CLo of the track groove 7B (edge portion of the inlet chamfer 20)so that the ball 4 is at the phase angle φ2 _(B) at which the ball 4loses a contact. Accordingly, a difference is made between the phaseangles φ2 _(A) and φ2 _(B).

The same reason applies to the phase angle φ1 at which the ball 4returns to the track groove 7 to start a contact state, and hence adevelopment view is omitted. However, as illustrated in FIG. 8, at thephase angle φ1 _(A) (see FIG. 8), the surface position 4 ao of the ball4 returns to the end of the contact locus CLo of the track groove 7A(edge portion of the inlet chamfer 20) to start a contact state.Meanwhile, at the phase angle φ1 _(B) (see FIG. 8), the surface position4 ao of the ball 4 returns to the end of the contact locus CLo of thetrack groove 7B (edge portion of the inlet chamfer 20) to start acontact state. As a result, when the fixed type constant velocityuniversal joint 1 taking the maximum operating angle is rotated in thecounterclockwise direction, as illustrated in FIG. 8, the range M_(A) inwhich the ball 4 loses a contact with the track groove 7A is smallerthan the range M_(B) in which the ball 4 loses a contact with the trackgroove 7B. In contrast, when the fixed type constant velocity universaljoint 1 is rotated in the clockwise direction, conversely to the casedescribed above, the range MA in which the ball 4 loses a contact withthe track groove 7A is larger than the range MB in which the ball 4loses a contact with the track groove 7B.

As described above, when the fixed type constant velocity universaljoint 1 according to this embodiment takes the maximum operating angle,the ball 4 located around the phase angle φ0, which moves toward theopening side of the track groove 7 of the outer joint member 2, comesoff the opening-side end portion (inlet chamfer 20) of the track groove7 of the outer joint member 2 and loses a contact with the track groove7, and the ball 4 comes off the back-side end portion of the trackgroove 9 of the inner joint member 3 and loses a contact with the trackgroove 9. However, as illustrated in FIG. 6a , the ball 4 located at thephase angle (φ=180°), which is opposed in a diameter direction to theball 4 located around the phase angle φ0, is set to have a contact onthe back side of the track groove 7 of the outer joint member 2, andhave a contact on the opening side of the track groove 9 of the innerjoint member 3. With this setting, the number of the balls 4 that bearload is increased, and a balance of internal forces is improved, therebybeing capable of maintaining strength and durability.

The characteristic configuration (1) of the fixed type constant velocityuniversal joint according to this embodiment is summarized below.Through use of the fixed type constant velocity universal joint of thecross track groove type as a base, the fixed type constant velocityuniversal joint according to this embodiment has the operation mode inwhich the ball loses a contact when the maximum operating angle istaken. Thus, even at the large operating angle at which the ball 4 losesa contact with the track groove 7 of the outer joint member 2, ascompared to the related-art axial track offset type, the moment and theforces applied to the cage 5 by the balls 4 act so as to be balanced,and hence the cage 5 is not significantly displaced from the bisectingplane. Accordingly, reduction in constant velocity characteristic andtransmission efficiency, and changes of internal forces can beminimized.

Further, when torque is applied in a range in which the balls arebrought into a contact state with respect to the track grooves, that is,a range of a normal operating angle having a small angle and a range offrom a medium angle to a large angle, owing to the structure in whichthe balls basically generate forces to push the cage in oppositedirections in the adjacent track grooves, the moment and the forcesapplied to the cage by the balls are balanced. In the range of from themedium angle to the large angle, there are variations in magnitude ofcontact forces between each ball and the track groove of the outer jointmember and between each ball and the track groove of the inner jointmember. However, as compared to the related-art axial track offset type,the moment and the forces applied to the cage by the balls are balanced,and hence the cage is stable near the bisecting plane, thereby beingcapable of obtaining a satisfactory constant velocity characteristic andtransmission efficiency.

Next, with reference to FIGS. 10 to FIG. 15, description is made of thecharacteristic configuration (2) of the fixed type constant velocityuniversal joint according to this embodiment, that is, a configurationin which, when the large operating angle is taken, the operating angleθ2 at which the ball 4 loses a contact with the track groove 9 of theinner joint member 3 is set to be larger than the operating angle θ1 atwhich the ball 4 loses a contact with the track groove 7 of the outerjoint member 2.

FIG. 10a is a longitudinal sectional view for illustrating a state inwhich the torque transmission ball loses a contact with the track grooveof the outer joint member when the fixed type constant velocityuniversal joint of FIG. 1a and FIG. 1b takes a large operating angle.FIG. 10b is a right-side view of FIG. 10a . FIG. 11 is a developmentview of the inner peripheral surface of the outer joint member, forillustrating a state in which the torque transmission ball loses acontact with the track groove of the outer joint member of FIG. 10b .FIG. 12 is an enlarged longitudinal sectional view for illustrating theportion F of FIG. 10a .

First, description is made of the operating angle θ1 at which the ball 4loses a contact with the track groove 7 of the outer joint member 2. Asillustrated in FIG. 10a and FIG. 10b , when the fixed type constantvelocity universal joint 1 according to this embodiment takes a largeoperating angle, the ball 4 moves toward the opening side of the trackgroove 7 of the outer joint member 2, and arrives at the edge portion ofthe inlet chamfer 20 of the track groove 7 so that the ball 4 loses acontact with the track groove 7 of the outer joint member 2. Theoperating angle at which the ball loses a contact corresponds to theoperating angle θ1 at which the ball 4 loses a contact with the trackgroove 7 of the outer joint member 2.

A positional relationship between the track grooves 7 of the outer jointmember 2 and the balls 4 at the time of the operating angle 01 isdescribed in detail with reference to FIG. 11 and FIG. 12. When theintermediate shaft 14 illustrated in FIG. 10b is rotated in thedirection (counterclockwise direction) indicated by the arrow, asillustrated in FIG. 11, a load range between the ball 4 and the trackgroove 7A or the track groove 7B is the contact locus CLo on the upperside of the drawing sheet of FIG. 11. FIG. 11 is an illustration of astate in which, among the balls 4 located in the track grooves 7A, thecenter Ob of the ball 4, which has moved to an end position in the axialdirection toward the opening side of the outer joint member 2, islocated at the phase angle φ0. Under this state, as illustrated in FIG.11 and FIG. 12, the surface position 4 ao of the ball 4 located in thetrack groove 7A arrives at an opening-side end of the contact locus CLo,that is, the edge portion of the inlet chamfer 20 so that the fixed typeconstant velocity universal joint 1 takes the operating angle θ1 _(A) atwhich the ball 4 loses a contact with the track groove 7A. Althoughillustration is omitted, the same holds true for a case of the trackgroove 7B. Under a state in which, among the balls 4 located in thetrack grooves 7B, the center Ob of the ball 4, which has moved to an endposition in the axial direction toward the opening side of the outerjoint member 2, is located at the phase angle φ0, the surface position 4ao of the ball 4 located in the track groove 7B arrives at anopening-side end of the contact locus CLo, that is, the edge portion ofthe inlet chamfer 20 so that the fixed type constant velocity universaljoint 1 takes the operating angle θ1 _(B) at which the ball 4 loses acontact with track groove 7B.

Regarding the operating angle θ1 at which the ball 4 loses a contactwith the track groove 7 of the outer joint member 2, when the center Obof the ball 4 is located at the phase angle φ0, the ball 4 moves to theend position in the axial direction toward the opening side of the outerjoint member 2. Accordingly, the operating angle θ1 is defined as anoperating angle at which the ball 4 loses a contact when the center Obof the ball 4 is located at the phase angle φ0. Further, the operatingangles θ1 _(A) and θ1 _(B) are collectively referred to as “theoperating angle θ1”. In Description and Claims, a phrase of “anoperating angle (θ1) at which the torque transmission ball loses acontact with the track groove of the outer joint member” is used withthe meaning described above.

As illustrated in FIG. 11, at the time of the operating angle θ1 _(A) atwhich the ball 4 located in the track groove 7A loses a contact with thetrack groove 7A, the track grooves 7B and the balls 4 that are locatedat the phase angle apart from the phase angle φ0 are in a contact stateat the contacts C1, and bear load.

Further, at a point in time when the ball 4 loses a contact with thetrack groove 7A of the outer joint member 2, as illustrated in FIG. 12,the surface position 4 ai of the ball 4 is within an axial range of thecontact locus CLi of the track groove 9A of the inner joint member 3,and the track groove 9A and the ball 4 are in a contact state at thecontact C3. Accordingly, at the point in time when the ball 4 loses acontact with the track groove 7A of the outer joint member 2 and whenthe ball 4 located with the same positional relationship returns to thetrack groove 7 of the outer joint member 2, the ball 4 can bear load onthe track groove 9 of the inner joint member 3.

Regarding the operating angle 01 at which the ball 4 loses a contactwith the track groove 7 of the outer joint member 2, similarly to theabove description of the phase angles φ1 _(A), φ1 _(B), φ2 _(A), and φ2_(B) and the ranges M_(A) and M_(B) at the time of the maximum operatingangle, in the track groove 7B having the inclination direction oppositeto that of the track groove 7A, due to a length difference in thecontact locus CLo, there is a slight difference between the operatingangles θ1 _(A) and θ1 _(B). Specifically, when the fixed type constantvelocity universal joint is rotated in the counterclockwise direction, arelation of θ1 _(A)>θ1 _(B) is satisfied. When the fixed type constantvelocity universal joint is rotated in the clockwise direction, arelation of θ1 _(A)<θ1 _(B) is satisfied. However, in both the rotatingdirections, a difference between θ1 _(A) and θ1 _(B) is about 0.5°. Thephrase of “the operating angle (θ1) at which the torque transmissionball loses a contact with the track groove of the outer joint member”described in Description and Claims also encompasses the meaningdescribed above.

Next, with reference to FIGS. 13 to FIG. 15, description is made of theoperating angle θ2 at which the ball loses a contact with the trackgroove of the inner joint member. FIG. 13a is a longitudinal sectionalview for illustrating a state in which the torque transmission ballloses a contact with the track groove of the inner joint member when thefixed type constant velocity universal joint of FIG. 1a and FIG. 1btakes a large operating angle. FIG. 13b is a right-side view of FIG. 13a. FIG. 14 is a development view of the inner peripheral surface of theouter joint member, for illustrating a positional relationship betweenthe track groove of the outer joint member and the torque transmissionball when the fixed type constant velocity universal joint takes theoperating angle in FIG. 13b . FIG. 15 is an enlarged longitudinalsectional view for illustrating the portion H of FIG. 13 a.

When the fixed type constant velocity universal joint takes an operatingangle larger than the operating angle θ1 at which the ball 4 loses acontact with the track groove 7 of the outer joint member 2, asillustrated in FIG. 13a and FIG. 13b , the ball 4 moves further to theback side of the track groove 9 of the inner joint member 3. The contactlocus CLi ends at the back-side end portion 3 a of the inner jointmember 3. When the surface position 4 ai of the ball 4 arrives at theend of the contact locus CLi, the ball 4 loses a contact with the trackgroove 9 of the inner joint member 3. The operating angle at which theball 4 loses a contact corresponds to the operating angle θ2 at whichthe ball 4 loses a contact with the track groove 9 of the inner jointmember 3.

A positional relationship between the track grooves 9 of the inner jointmember 3 and the balls 4 at the time of the operating angle θ2 isdescribed in detail with reference to FIG. 15. When the intermediateshaft 14 illustrated in FIG. 13b is rotated in the direction(counterclockwise direction) indicated by the arrow, a load rangebetween the ball 4 and the track groove 7A or the track groove 7B is thecontact locus CLi on the upper side of the drawing sheet of FIG. 14.FIG. 15 is an illustration of a state in which, when the surfaceposition 4 ai of the ball 4, which has lost a contact with the trackgroove 7A of the outer joint member 2, arrives at the end of the contactlocus CLi and the ball 4 loses a contact with the track groove 9A of theinner joint member 3, the center Ob of the ball 4 at this time islocated at the phase angle φ0. The operating angle under this statecorresponds to an operating angle θ2 _(A) at which the ball 4 loses acontact with the track groove 9A of the inner joint member 3.

Although illustration is omitted, the same holds true for a case of thetrack groove 9B. When the surface position 4 ai of the ball 4, which haslost a contact with the track groove 7B of the outer joint member 2,arrives at the end of the contact locus CLi and the ball 4 loses acontact with the track groove 9B of the inner joint member 3, the centerOb of the ball 4 at this time is located at the phase angle φ0. Theoperating angle under this state corresponds to an operating angle θ2_(B) at which the ball 4 loses a contact with the track groove 9B of theinner joint member 3. The operating angle θ2 at which the ball 4 loses acontact with the track groove 9 of the inner joint member 3 is alsodefined as the operating angle at which the ball 4 loses a contact whenthe center Ob of the ball 4 is located at the phase angle φ0. Further,the operating angles θ2 _(A) and θ2 _(B) are collectively referred to as“operating angle θ2”. In Description and Claims, a phrase of “anoperating angle (θ2) at which the torque transmission ball loses acontact with the track groove of the inner joint member” is used withthe meaning described above.

Similarly to the above-mentioned operating angles θ1 _(A) and θ1 _(B) atwhich the ball loses a contact with the track groove of the outer jointmember, in the track groove 9B having the inclination direction oppositeto that of the track groove 9A, due to a length difference in thecontact locus CLi, there is also a slight difference between theoperating angles θ2 _(A) and θ2 _(B) at which the ball 4 loses a contactwith the track groove 9 of the inner joint member 3. Specifically, whenthe fixed type constant velocity universal joint is rotated in thecounterclockwise direction, a relationship of θ2 _(A)>θ2 _(B) issatisfied. When the fixed type constant velocity universal joint isrotated in the clockwise direction, a relationship of θ2 _(A)<θ2 _(B) issatisfied. However, in both the rotating directions, a differencebetween θ2 _(A) and θ2 _(B) is about 0.5°. The phrase of “the operatingangle (θ2) at which the torque transmission ball loses a contact withthe track groove of the inner joint member” described in Description andClaims also encompasses the meaning described above.

In the fixed type constant velocity universal joint 1 according to thisembodiment, the operating angle θ2 at which the torque transmission ball4 loses a contact with the track groove 9 of the inner joint member 3 isset to be larger than the operating angle θ1 at which the torquetransmission ball 4 loses a contact with the track groove 7 of the outerjoint member 2. With this setting, when the ball 4, which has come offthe track groove 7 of the outer joint member 2 and lost a contact,returns to the track groove 7 again to start a contact state, the ball 4retained in the pocket 5 a of the cage 5 is guided to the track groove 9of the inner joint member 3. Thus, the ball 4 can smoothly return to thetrack groove 7 of the outer joint member 2. That is, when the ball 4returns to the track groove 7 of the outer joint member 2, the load ofthe ball 4 can be borne on the track groove 9 of the inner joint member3. Accordingly, without increasing the internal forces, damage to theopening-side end portion of the outer joint member 2 can be prevented,thereby being capable of improving strength and durability.

A minimum value of a difference between the operating angle θ2 at whichthe torque transmission ball 4 loses a contact with the track groove 9of the inner joint member 3 and the operating angle θ1 at which thetorque transmission ball 4 loses a contact with the track groove 7 ofthe outer joint member 2 is set to 3°. A maximum value of the differenceis set to an angle at which the ball 4 can keep a contact with aradially outer side of the cage. When the minimum value is set to besmaller than three degrees, there is a fear in that a contact ellipsebetween the ball 4 and the track groove 9 of the inner joint member 3climbs on the back-side end portion 3 a (see FIG. 12) of the trackgroove 9. Meanwhile, when the maximum value is set to an angle largerthan the angle at which the ball 4 can keep a contact with the radiallyouter side of the cage 5, there is a risk in that the ball 4 is notretained in the pocket 5 a of the cage 5 and noise is generated.

The characteristic configuration (2) of this embodiment described aboveis summarized below. When the ball 4, which has come off the trackgroove 7 of the outer joint member 2 and lost a contact, returns to thetrack groove 7 of the outer joint member 2, the load of the ball 4 canbe borne on the track groove 9 of the inner joint member 3. Accordingly,without increasing the internal forces, damage to the opening-side endportion of the outer joint member 2 can be prevented, thereby beingcapable of improving strength and durability.

As described above, the fixed type constant velocity universal joint 1according to this embodiment has the operation mode in which, when themaximum operating angle is taken, the ball loses a contact in the fixedtype constant velocity universal joint of the cross track groove type.Thus, even at the large operating angle at which the ball 4 loses acontact with the track groove 7 of the outer joint member 2, the momentand the forces applied to the cage 5 by the balls 4 act so as to bebalanced, and hence the cage 5 is not significantly displaced from thebisecting plane. The characteristic configuration (2) is combined withthe advantageous characteristic configuration (1) that is basicallyprovided to the fixed type constant velocity universal joint of thecross track groove type and is capable of minimizing reduction inconstant velocity characteristic and transmission efficiency, andminimizing changes of internal forces. Through the combination of theconfigurations, there can be achieved the fixed type constant velocityuniversal joint dramatically improved in constant velocitycharacteristic, transmission efficiency, changes of internal forces,strength, and durability.

In the embodiment described above, there is exemplified the fixed typeconstant velocity universal joint 1 in which the track grooves 7 of theouter joint member 2, which are inclined in the circumferentialdirection, each comprise the first track groove portion 7 a having thearc-shaped raceway center line Xa having the curvature center at thejoint center 0, and the second track groove portion 7 b having thelinear raceway center line Xb, and in which the track grooves 9 of theinner joint member 3, which are inclined in the circumferentialdirection, each comprise the first track groove portion 9 a having thearc-shaped raceway center line Ya having the curvature center at thejoint center O, and the second track groove portion 9 b having thelinear raceway center line Yb. However, the present invention is notlimited thereto. The present invention is also applicable to a fixedtype constant velocity universal joint in which the track grooves 7 ofthe outer joint member 2 inclined in the circumferential direction eachhave, in an entire axial region thereof, the arc-shaped raceway centerline X having the curvature center at the joint center O, and in whichthe track grooves 9 of the inner joint member 3 inclined in thecircumferential direction each have, in an entire axial region thereof,the arc-shaped raceway center line Y having the curvature center at thejoint center O.

The present invention is not limited to the above-mentioned embodiments.As a matter of course, the present invention can be carried out invarious modes without departing from the spirit of the presentinvention. The scope of the present invention is defined in Claims, andencompasses equivalents described in

Claims and all changes within the scope of Claims.

DESCRIPTION OF REFERENCE SIGNS

-   1 fixed type constant velocity universal joint-   2 outer joint member-   3 inner joint member-   3 a end portion-   4 torque transmission ball-   5 cage-   5 a pocket-   6 spherical inner peripheral surface-   7 track groove-   7 a first track groove portion-   7 b second track groove portion-   8 spherical outer peripheral surface-   9 track groove-   9 a first track groove portion-   9 b second track groove portion-   12 spherical outer peripheral surface-   13 spherical inner peripheral surface-   20 inlet chamfer-   CLo contact locus-   CLi contact locus-   M plane-   N axis of joint-   O joint center-   Ob center of ball-   P plane-   Q plane-   W distance-   X raceway center line-   Xa raceway center line-   Xb raceway center line-   Y raceway center line-   Ya raceway center line-   Yb raceway center line-   θmax maximum operating angle-   θ1 operating angle at which contact is lost-   θ2 operating angle at which contact is lost-   φ0 phase angle-   φ1 phase angle-   φ2 phase angle

1. A fixed type constant velocity universal joint, comprising: an outerjoint member, which has a plurality of track grooves being formed in aspherical inner peripheral surface of the outer joint member andextending substantially in an axial direction, and has an opening sideand a back side apart from each other in the axial direction; an innerjoint member, which has a plurality of track grooves being formed in aspherical outer peripheral surface of the inner joint member andextending substantially in the axial direction so as to be opposed tothe track grooves of the outer joint member; torque transmission ballsincorporated in pairs of the track grooves opposed to each other; and acage configured to retain the torque transmission balls in pockets, thecage comprising: a spherical outer peripheral surface to be guided bythe spherical inner peripheral surface of the outer joint member; and aspherical inner peripheral surface to be guided by the spherical outerperipheral surface of the inner joint member, wherein a raceway centerline (X) of the track groove of the outer joint member comprises atleast an arc-shaped portion having a curvature center that has no offsetwith respect to a joint center (O) in the axial direction, wherein aplane (M) including the raceway center line (X) and the joint center (O)is inclined with respect to an axis (N-N) of the joint, and the trackgroove is formed with such an inclination direction of the plane (M)that the track grooves adjacent to each other in a circumferentialdirection are inclined in opposite directions, wherein a raceway centerline (Y) of the track groove of the inner joint member is formed so asto be mirror-symmetric with the raceway center line (X) of the pairedtrack groove of the outer joint member with a plane (P) including thejoint center (O) and being orthogonal to the axis (N-N) of the joint ina state of an operating angle of 0° as a reference, and wherein, when alarge operating angle is taken, an operating angle (θ2) at which thetorque transmission ball loses a contact with the track groove of theinner joint member is larger than an operating angle (θ1) at which thetorque transmission ball loses a contact with the track groove of theouter joint member.
 2. The fixed type constant velocity universal jointaccording to claim 1, wherein the raceway center line (X) of the trackgroove of the outer joint member comprises the arc-shaped portion havingthe curvature center that has no offset with respect to the joint center(O) in the axial direction, and a portion different in shape from thearc-shaped portion, wherein the arc-shaped portion and the portiondifferent in shape from the arc-shaped portion are smoothly connected toeach other at a connection point (J), and wherein the connection point(J) is located more on the opening side of the outer joint member thanthe joint center (O).
 3. The fixed type constant velocity universaljoint according to claim 1, wherein the portion different in shape islinear.
 4. The fixed type constant velocity universal joint according toclaim 1, wherein the operating angle (θ2) at which the torquetransmission ball loses a contact with the track groove of the innerjoint member is larger, by 3° or more, than the operating angle (θ1) atwhich the torque transmission ball loses a contact with the track grooveof the outer joint member.
 5. The fixed type constant velocity universaljoint according to claim 1, wherein an upper limit of the operatingangle (θ2) at which the torque transmission ball loses a contact withthe track groove of the inner joint member is set to a value enablingthe torque transmission ball to keep a contact with the pocket of thecage.
 6. The fixed type constant velocity universal joint according toclaim 1, wherein the number of the torque transmission balls is set tobe equal to or larger than eight.